Experiments are proposed which will evaluate interventions which are thought to alter infarct size: we will employ an autoradiographic procedure which expresses infarct size as a percentage of myocardium at risk. This procedure, developed in this laboratory, involves occluding the coronary artery of a closed chest, anethesized dog and infusing radiolabeled microspheres one minute later into the systemic circulation. The dog is allowed to recover and the infarct develop. Forty-eight hours later, the dog is reanethesized and the heart removed, sectioned, and stained to visualize the necrotic tissue. The myocardium at risk is determined by visualizing the distribution of the microspheres by autoradiography. A sharp blood flow border is always seen between the normally perfused and the ischemic zone with this technique and can be used as a reproducible landmark; the region at risk is considered to be the non-perfused region. The shape and size of the infarct on each heart slice is then compared to that of the risk zone on the x-ray film. Five drugs will be examined to see if infarct size can be reduced in this model and, if so, the model will readily reveal if salvage is occuring at the lateral borders of the infarct or subepicardially only. Experiments are also proposed which will use the auto radiographic procedure to examine the degree of overlap between two adjacent coronary branches. One branch will receive microspheres while another branch will receive an infusion of a fluorescent dye. Regions of overlap will be revealed by tissue which is both fluorescent and contains microspheres.